1. Field of the Invention
This invention relates generally to storage volumes with multiple hard disk drives or solid state drives, and, more particularly, to increasing write speed on a storage volume while providing data protection.
2. Description of the Background Art
Most RAID storage devices provide protection from disk failure. If a disk fails on a RAID volume, all data on the volume is still available. This protection comes from either storing a redundant copy of the volume's data (e.g., RAID 1 and RAID 1+0) or calculating and storing parity information for each block of data on the volume (e.g., RAID 4, 5, 6, and DP). When a disk fails on one of these RAID volumes, the volume's data can be recovered by either reading it from the redundant copy or creating the data that was on the failed disk by using the remaining disks and the parity information stored for each block of data.
On RAID volumes that offer data protection, there are extra steps that must be taken every time data is written to the volume in order provide such data protection. These steps are either writing the redundant copies of data out to additional disks or calculating and writing out the parity information. With hard disks (i.e., disks with mechanical arms and rotating media), these steps are only a small percentage of the total time taken for a write, and they have only a small impact on the write performance of a RAID volume. With faster disks, such as SSD (Solid State Disks with use memory chips rather than rotating media), the percentage of time taken for the extra steps increases. With these disks, the extra steps required for write operations result in write performance that is dramatically slower than read performance, and there is a need to increase write speed on such disks while still performing the extra steps that provide data protection.